Accumulated Other Comprehensive Income (Loss) - Schedule of Changes in Accumulated Other Comprehensive Income Loss (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Jun. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance, net of tax	$ 40,700	$ (18,200)	$ (2,100)	$ 83,315	$ (2,100)
Other comprehensive income (loss) before reclassifications:
Change in fair value of derivatives	31,600	47,100		35,700	3,700
Foreign currency translations	(200)	(1,600)		(2,500)	(1,300)
Income tax effect	(11,500)	(16,900)		(12,800)	(1,200)
Net of tax	19,900	28,600		20,400	1,200
Amounts reclassified from accumulated other comprehensive income:
Operating revenue: oil/natural gas production	39,900	(1,300)		107,100	(17,600)
Derivative expense, net					(1,500)
Income tax effect	(14,400)	500		(38,500)	7,000
Net of tax	25,500	(800)		68,600	(12,100)
Other comprehensive income (loss), net of tax	(5,600)	29,400		(48,200)	13,300
Ending balance, net of tax	35,057	11,200	(18,200)	35,057	11,200
Cash Flow Hedges [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance, net of tax	46,500	(17,800)	(1,400)	86,800	(1,400)
Other comprehensive income (loss) before reclassifications:
Change in fair value of derivatives	31,600	47,100		35,700	3,700
Foreign currency translations	0	0		0	0
Income tax effect	(11,500)	(16,900)		(12,800)	(1,200)
Net of tax	20,100	30,200		22,900	2,500
Amounts reclassified from accumulated other comprehensive income:
Operating revenue: oil/natural gas production				107,100
Derivative expense, net					(1,500)
Income tax effect	(14,400)	500		(38,500)
Net of tax	25,500	(800)		68,600	(12,100)
Other comprehensive income (loss), net of tax	(5,400)	31,000		(45,700)	14,600
Ending balance, net of tax	41,100	13,200	(17,800)	41,100	13,200
Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Amounts reclassified from accumulated other comprehensive income:
Income tax effect			7,000
Foreign Currency Items [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance, net of tax	(5,800)	(400)	(700)	(3,500)	(700)
Other comprehensive income (loss) before reclassifications:
Change in fair value of derivatives	0	0		0	0
Foreign currency translations	(200)	(1,600)		(2,500)	(1,300)
Income tax effect	0	0		0	0
Net of tax	(200)	(1,600)		(2,500)	(1,300)
Amounts reclassified from accumulated other comprehensive income:
Operating revenue: oil/natural gas production	0	0		0	0
Derivative expense, net					0
Income tax effect	0	0		0	0
Net of tax	0	0		0	0
Other comprehensive income (loss), net of tax	(200)	(1,600)		(2,500)	(1,300)
Ending balance, net of tax	$ (6,000)	$ (2,000)	$ (400)	$ (6,000)	$ (2,000)